1. Field of the Invention
The present invention relates to the cementing of wells, such as oil, gas or water wells. The process of the invention may be employed in primary cementing, i.e., the cementing of casing in the well, or in secondary cementing, i.e., remedial cementing operations, such as squeeze cementing to repair leaks or seal off loss circulation or high pressure zones.
2. Description of the Prior Art
Heretofore, cement slurries for use in cementing wells have been prepared by continuously mixing a stream of dry powdered cement with a stream of water, the rates of flow of the two streams being controlled by automatic control equipment responsive to the density of the slurry to provide a cement slurry having a selected density or composition. Also, cement additives such as retarders, have been blended with dry cement which is thereafter mixed with water to form the slurry. Even small variations in the percentage of retarder or other additive in the slurry, or small variations in the distribution of the retarder in the dry cement, can greatly affect the performance of the slurry. Improper amounts of additive can lead to serious problems such as reduced thickening time, flash setting, loss of compressive strength, and others. Processes for determining the percentage of additive in the dry cement blend have been practiced. Such process is disclosed in U.S. Pat. No. 3,565,553 issued Feb. 23, 1971 to Garcia et al. In this process a tracer dye is blended with the additive and this mixture is thereafter blended with the dry cement, a test sample of the total mix being then mixed with a liquid to dissolve the dye and a spectro-photometric analysis is made to determine the percentage of the dye and thus the additive in the dry cement mix.
Another such process is disclosed in U.S. Pat. No. 3,615,223, issued Oct. 26, 1971, to James E. Burroughs et al. In this method, the distribution of the retarder in the dry ingredients of an oil well cementing composition is determined by mixing a test sample of the composition with an agent to react with or dissolve the retarder, and a spectrophotometric analysis is made to determine the percentage of the retarder in the mix.
It has also been proposed to dissolve a cement additive in water to form a solution that is thereafter mixed with dry cement to form a slurry.